Young children with untreated asthma who are also overweight may face more days of symptoms each year than their healthy weight peers, a new study suggests.

In the study, researchers found that preschoolers with a body mass index (BMI) beyond the 84th percentile who weren’t using an inhaler had 70 percent more days with asthma symptoms per year than untreated healthy weight children.

These children suffered 37 more symptom-days—more than five extra weeks—per year than their healthy-weight peers. Researchers also found that untreated children who were overweight had more asthma attacks than untreated peers of a healthy weight.

Asthma affects almost 1 in 10 children in the US and is a leading cause of emergency room visits and hospitalizations in preschoolers.

There is some good news: obesity doesn’t seem to lessen the effectiveness of corticosteroid inhalers, the standard treatment to ease asthma symptoms such as shortness of breath, coughing, and chest pain, says lead author Jason Lang, a pediatric lung specialist and director of the Duke University Children’s Pulmonary Function Laboratory.

When used daily, inhalers reduced the number of symptom-days and asthma attacks in both healthy and overweight children, and may be even more protective to overweight children, the authors write.

“The impact of overweight and obesity on asthma has not been studied in the youngest asthma patients, and this finding is the opposite of what has been seen in older kids and adults who are overweight,” Lang says.

“Reports in older children and adults with asthma who are overweight have shown a poor response to inhaled corticosteroids to manage their asthma. This study suggests either pathways of inflammation are a bit different in preschool-aged patients, or that it takes years for obesity to reduce the effectiveness of steroid inhalers.”

As the researchers report in the Journal of Allergy and Clinical Immunology, the study analyzed data from three randomized, controlled clinical trials conducted between 2001 and 2015 called INFANT, PEAK, and MIST that included 736 children. One-third of participants had a BMI above the 84th percentile.

Some trial participants were randomly assigned to use inhalers daily while some used them intermittently; some received placebos, and some received no treatment.

The researchers believe this is the first study to look at whether obesity has an effect on asthma severity and how well inhalers work for preschoolers, but the study does have limitations, including that it was a retrospective analysis, one that searches back in time to seek patterns.

Prospective, or forward-looking, research with a larger number of children could offer more insights into the best asthma treatments for overweight preschoolers and include strategies that address weight loss, the researchers say.

“Weight does not hamper the effectiveness of inhaled steroids in preschoolers, but this study provides clear evidence that maintaining a healthy weight in preschoolers may be an effective strategy for controlling asthma.”